Artificial leather or leather-like have been widely used in the production of clothing and leather shoes. Currently the leather or leather-like manufacturing processes utilize a variety of combinations of different making processes according to the different uses of the product. In general, a product whose appearance is like leather is made by coating the surface of a selected substrate with one or multiple layers of synthetic resins containing various additives. The wet-coagulation method is normally used to manufacture artificial leather or leather-like flakes. The process mainly comprises the steps of: coating a substrate with an organic solvent-based resin composition; immersing the treated substrate in a immersion tank with an aqueous solution of dimethylformamide (DMF); curing the surface of the treated substrate from the previous step in a water tank; forming an artificial leather substrate by drying out the product from the previous step in a drying oven; and bonding a surface layer which is made separately to the finished substrate using a binding agent.
While during the wet-coagulation process, many organic solvents, such as toluene, xylene, acetone, methyl ethyl ketone (MEK), ethyl acetate, DMF, etc., are used extensively to make the substrate, surface layer or binding agent; and many chemicals, such as plasticiser vapours (dioctyl phthalate, etc.), vinyl chloride, hydrogen chloride, organic solvents, lead, toxic dioxin, etc., are used or produced in the utility of polyvinyl chloride (PVC) related techniques. The above hazardous chemical substances pose various threats to human health, which is discussed in the following. Aromatic solvent such as toluene has toxic effect on hematopoietic organs. And long-term exposure to high concentrations of aromatic solvent may cause shock because of acute poisoning, or cause the reduction in platelet or white blood cell because of chronic poisoning, which leads to a variety of symptoms of illness. Xylene is highly flammable and explosive, which is easily ignited by heat, sparks or flames and becomes the cause of fire. Butanol, MEK, acetone, ethyl acetate, DMF and other solvents have considerable toxic side effects on human health. Ethyl acetate may cause narcosis or eye irritation. DMF which is the most extensively used solvent in the production of artificial leather may cause acute irritation to skin and ophthalmic mucous membranes. Inhalation of high concentrations of DMF vapour may cause nausea because of respiratory tract irritation. And frequent exposure to DMF, via dermal absorption, may lead to hepatic dysfunction. In addition, organic solvents may have negative effects on a woman's reproductive health. Although most factories are now using the solvent treatment equipment to recycle the solvent, a small amount of solvent waste from wet-style production process and a large amount of solvent waste from dry-style production process are still discharged directly into the surrounding water and air, which heavily pollutes the local environment and poses significant threats to the local production, life and public health.
In order to solve the above issues, new processes of manufacturing artificial leather or leather-like have been developed, e.g., a process in which organic solvents are replaced with water based materials. The process of making artificial leather which utilizes a water based resin is safe and clean, and the finished product is non-toxic as well as green. But there exist quite a few issues on the popularization of the process. One issue is that water based resin has inappropriate physical properties, such as high value of surface tension which causes spreading difficulty, slow volatility which causes drying difficulty, etc. Another issue is that there still exist quite a few problems during production, such as the equipment problem, the technical problem of leather processing, the problem of water based additive material matching, the problem of whether or not release paper is applicable, etc. In addition, the finished product feels uncomfortable against the skin and needs to be improved in terms of properties, such as resistance to wear, resistance to scratch, resistance to heat, resistance to durability, resistance to acid and alkali, resistance to solvent, resistance to wet abrasion, tensile strength, etc. Another evolved process of making artificial leather involves roller or knife coating release paper with a foamed mixture which is formed by fast stirring a few quantitatively mixed molecular designed compounds at an appropriate temperature. The artificial leather made through the process is environmentally friendly and has excellent physical and chemical properties. But the process involves a very long-time maturing step, uses equipment with huge footprint, has low productivity, is difficult to industrialize.